Accuracy of Combined Anteversion in the Combined Anteversion Technique with Image-free Navigated Total Hip Arthroplasty

In recent literatures dealing with optimization of prosthetic alignment in total hip arthroplasty (THA), the concept of combined anteversion (CA), which is the sum of acetabular anteversion (AV) and femoral antetorsion (AT), has been addressed. Widmer attempted to determine the optimal CA using a computer simulation study . He proposed the “new safe zone” for the CA value to achieve essential range of motion while avoiding prosthetic impingement. On the other hand, Dorr described the combined anteversion technique (CA technique) to determine both cup and stem alignment during THA procedure . He proposed the so-called “stem-first” procedure for the CA technique in which the stem is set first, and cup alignment is determined to consider the target CA value. In our recent clinical practice, we have been using an image-free THA navigation system (OrthoPilot THA Pro; B/BRAUNAesculap, Germany) to achieve improved overall alignment with both stem and cup . In the present study, the femur was prepared first with the target angle corresponding to the native femoral AT, and the cup AV was decided considering the CA calculated with Widmer’s formula (37.3°= cup AV + 0.7 stem AT) using an image-free navigation system.The purpose of this study was to evaluate the accuracy of CA by using the CA technique with image-free navigated THA.